1. Known or suspected pregnancy;
2. the use of oral contraceptives (i.e. ProveraŽ, MirenaŽ, Nuva ringŽ ect.) in the last three months;
3. smoking habit;
4. subjects suffering from epilepsy;
5. diabetes mellitus;
6. gastrointestinal, hepatic, renal, and/or pulmonary diseases;
7. abnormal history;
8. use of other investigational drugs within 3 months and/or use of hormonal preparations-other then dose used for COH-within 1 month prior to the start of the study.

Duration of the luteal phase. Every subject will undergo an end of trial visit. In this visit the subjects will hand over a paper on wich she will write down the onset of the menstuation. These data will be put into a excel database.

- Secondary outcome

Endocrine profiles. Blood will be sampled every other day in the luteal phase from the day of the positive LH test until day LH+14.